Why did the Roman civilization begin?

As legend has it, there were two babies left out in the fields, Romulus and Remus. They were found and raised by a she-wolf, and when they got old enough they built there own cities, not being able to agree on one spot to build one city. Remus decided to jump over Romulus's wall mocking him for how easily he could get into his city. Romulus killed Remus, and created the city of Rome.

That's just the legend though. Nobody knows how it actually started.